Injection of anhydrous ammonia into the soil is a commonly used method of supplying nitrogen fertilizer to grain and other crops using an applicator vehicle pulled by a tractor. An ammonia storage tank is pulled behind the applicator. A hose connects the storage tank to the distribution system on the applicator. The distribution system splits the ammonia into separate lines which feed multiple knives. These knives are lowered into the soil several inches and ammonia is injected into the ground at the bottom of the knives as the knives are pulled through the soil.
It is normally desired that ammonia be applied uniformly over a field. One of the main problems in achieving this uniformity is difficulty in controlling a stream of mixed liquid and gaseous ammonia. Gaseous ammonia causes most flow sensors to supply incorrect data. Many anhydrous ammonia application systems use a heat exchanger to cool the ammonia flow from the storage tank to condense vapor which has been created by friction in the hose from a nurse tank.
Part of the liquid ammonia is used as a refrigerant to cool the inlet liquid stream. This is accomplished in a heat exchanger which mechanically separates the main stream of inlet liquid ammonia from a stream of coolant ammonia. Typically, the coolant stream is taken from the main stream after the heat exchanger. The coolant passes through a restriction and loses pressure and temperature before it enters coolant side of the heat exchanger. A portion of the coolant stream evaporates in the heat exchanger, taking heat from the main stream. This cools the main stream and condenses incoming ammonia vapor back to Liquid.
Most current anhydrous ammonia application systems follow the heat exchanger with a flow sensor which measures the rate of flow of incoming liquid ammonia. After the flow sensor this flow goes through a servo valve which regulates the total flow rate. At the servo valve the anhydrous experiences a pressure drop which causes some of it to vaporize. The resulting mixture of liquid and vapor phases is not easily split among the multiple injection locations.
Crops such as corn are planted by planters with a selected space between rows. The spacing between rows varies depending upon a number of factors including crop to be grown, soil conditions, and hours of sun shine during the crop growing period. The applicator usually has the number of soil cutting knives required to apply ammonia to the number of rows planted by a planter during each pass through a field. With automated tractor guidance system employed by some farmers, the number of soil cutting knives on an ammonia applicator may not be limited by the number of planter row units on the planter. A large applicator tool bar may require multiple metering manifolds.